1. Field of the Invention
The present invention relates to aquariums and more specifically, to an aquarium heater for aquarium, which uses positive temperature coefficient element as a heat source to keep water warm.
2. Description of the Related Art
To keep the water in an aquarium warm, a heater is usually used. A conventional heater for this purpose generally comprises a ceramic coil holder, a heating coil wound round the ceramic coil holder, and a housing surrounding the ceramic coil holder and the heating coil. When the heating coil is electrically connected to generate heat, heat energy is transferred through the housing to the water in the aquarium. Similar designs are seen in U.S. Pat. No. 7,293,914, entitled “Temperature detecting heater with indicating structure for aquarium”, and U.S. Pat. No. 6,097,007, entitled “Aquarium water temperature controller”, both issued to the present inventor.
Convention heating coil type heater designs need a circuit board with a temperature control loop to avoid overheating. The installation of this temperature control loop increases the dimension of the heater and complicates its installation procedure, resulting in a high cost.
A bimetal temperature switch may be used with an aquarium heater as foolproof means. However, the foolproof action may fail due to a contact failure (such as short circuit), causing an accident. An improvement in this regard is necessary.
PTC (Positive temperature coefficient) materials that experience an increase in electrical resistance when their temperature is raised. The higher the coefficient, the greater an increase in electrical resistance for a given temperature increase. Therefore, the heating temperature of a PTC element is constant. PTC materials have been intensitively used in heaters for electric mosquito repeller and starters for refrigerators where a constant temperature level is required. Therefore, it is the scope of discussion to apply a PTC element to an aquarium heater for a better performance.